linux-kernel - [PATCH] KVM: arm/arm64: don't set vtimer->cnt_ctl in kvm_arch_timer

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Date:   Tue, 12 Dec 2017 23:00:07 -0800
From:   Jia He <hejianet@...il.com>
To:     Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu
Cc:     linux-kernel@...r.kernel.org, Jia He <hejianet@...il.com>,
        Jia He <jia.he@...-semitech.com>
Subject: [PATCH] KVM: arm/arm64: don't set vtimer->cnt_ctl in kvm_arch_timer_handler

In our Armv8a server (qualcomm Amberwing, non VHE), after applying
Christoffer's timer optimizing patchset(Optimize arch timer register
handling), the guest is hang during kernel booting.

The error root cause might be as follows:
1. in kvm_arch_timer_handler, it reset vtimer->cnt_ctl with current
cntv_ctl register value. And then it missed some cases to update timer's
irq (irq.level) when kvm_timer_irq_can_fire() is false
2. It causes kvm_vcpu_check_block return 0 instead of -EINTR
	kvm_vcpu_check_block
		kvm_cpu_has_pending_timer
			kvm_timer_is_pending
				kvm_timer_should_fire
3. Thus, the kvm hyp code can not break the loop in kvm_vcpu_block (halt
poll process) and the guest is hang forever

Fixes: b103cc3f10c0 ("KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit")
Signed-off-by: Jia He <jia.he@...-semitech.com>
---
 virt/kvm/arm/arch_timer.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index f9555b1..bb86433 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -100,7 +100,6 @@ static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id)
 	vtimer = vcpu_vtimer(vcpu);
 
 	if (!vtimer->irq.level) {
-		vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl);
 		if (kvm_timer_irq_can_fire(vtimer))
 			kvm_timer_update_irq(vcpu, true, vtimer);
 	}
-- 
2.7.4